Cathode



G. F. ROUSE I Dec. 21, 1948.

CATHODE Filed June 12, 1945 FIG. 1.

INVENTOR.

GLENN FZROUSE. Y

kw QM.

Patented Dec. 21 1948 UNITED STATES PATENT OFFICE CATHODE Glenn F. Rouse, Long Branch, N. J. Application June 12, 1943, Serial No. 490,624

3 Claims. (Cl. 2s0-27.5)

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

a This invention relates to electron emitting cathodes, particularly of the oxide type.

Oxide-coated cathodes have long been known, and have the advantage of copious electron emission at relatively low temperature. They have beenused very successfully in receiver tubes, but have not proved equally successful in transmitter tubes. It has been customary to use a smooth metal cathode can coated with the oxide material. With such a cathode, particularly when used for transmission, there is a tendency for the outside coating to scale or flake off. Another diffic-ulty is the tendency for some of the oxide material to move from the cathode to the grid, thus encouraging electron emission from the grid, a difficulty known as grid contamination. Furthermore, the total amount of emission depends on the cathode area, and that in turn is dependent on the diameter and length of the cylinder. when using a cylindrical cathode.

The primary object of the present invention to generally improve electron emission tubes, and particularly oxide-type cathodes. A more particular object is to provide a cathode of the oxide type "which will be characterized by long life, and will not be subject to flaking off of the oxide material. An ancillary object is to devise an oxidetype cathode which will minimize the eifect of grid contamination. Another important object of the present invention is to provide a cathode having increased electron emission area without necessitating a corresponding increase in the apparent physical area of the cathode (for example, the diameter and length of the cylinder when using a cylindrical cathode).

To accomplish the foregoing, and other objects which will hereinafter appear, my invention resides in the electrode elements and their relation one tothe other, as hereinafter are more particularly described in the specification and sought to bev defined in the claims. The specification is. accompanied by a drawing in which: I Figure 1 is a horizontal section through an electrode assembly embodying features of my invention, said section being taken approximately in the plane of the line i l of Figure 2;

'Figure'z is a vertical section taken approximately in theplane of the line 2-2 of Figure 1;

Figure' '3 illustrates a piece of wire screen used as'abase of foundation for the cathode;

Figure 4 shows how the screen may be bent 2 to cylindrical configuration to provide a cylindrical cathode;

Figure 5 is a fragmentary horizontal section drawn to enlarged scale through the wire screen,

after coating the same with electron emissive material, said section being taken between horizontal wires of the screen; and

Figure 6 is a similar section taken at one of the horizontal wires of the screen.

Referring to the drawing, and more particularly to Figures 1 and 2, the electrode assembly there shown comprises a cathode generally designated l2, surrounded by a grid l4, and an anode iii.

In order to simplify the drawing, only the edge wires of the cathode and grid are shown in Figure 2, and the coating of electron emissive material has also been omitted in Figure 2. It will be understood that in practice the electrode assembly is enclosed within an evacuated glass envelope, the various electrodes being supported by suitable lead-ins passing through sealed glass stems. The present invention centers primarily in the structure of the cathode I2.

One characteristic feature of my improved cathode is that the foundation or base is rough or irregular, in order to give the coating a rough or irregular surface, so as to increase the electron emitting area for a given size of cathode base. This is clearly shown in Figure 5, in which it will be seen that the outside surface has indentations 20, which give the same a kind of Waflie-like surface. Although this may be done by using a rough or irregular sheet metal surface for the foundation, I have found that it is simpler, cheaper, and more convenient to employ a wire screen such as that shown at 22 in Figure 3. Such a screen has the important additional advantage that a coating sprayed or otherwise applied thereon will tenaciously adhere to the screen. for it penetrates the interstices of the screen and surrounds the wires of the same, instead of merely lying on the surface, as would be the case with sheet metal.

In the present case, the cathode is cylindrical, and it is necessary to bend the wire screen 22 from the flat condition shown in Figure 3 to the cylindrical shape shown in Figure 4. The upper end is preferably closed, as by means of a disc of metal 24, best shown in Figure 2. The cathode is heated by means of a heater filament 26 disposed inside the cathode can. It will be understood that when making a cylindrical cathode as here shown, the bending of the cathode screen is preferably completed before applying the elec--' tron emissive coating thereto.

purposes, I prefer to avoid these holes because" the object in view is maximum electron emittin surface, and this is best obtained by reducing the thickness of the coating in the" interstices to a minimum, without however actually forming. openings through the screen.

In some special cases it may be; deemed desirable to purposely provide holes through thecath ode. An example of this is when it is sought to intentionally heat the grid. IE in order to. help control or minimize the effect of grid: emission. In. such case, the provision of holes through the grid will permit some of the radiant heatfrom the filament to pass through the screen, so as to heat the grid to so high a temperature as to clean it off.

The nature of the surface obtained on the cathode depends not only onthe thickness of the coating, but also on the dimensional characteristics of the screen. For example, a coarse mesh.

4 ates which are later reduced to the oxides. The carbonates are mixed with a cellulose acetate binder or adhesive, and the mixture is diluted by means of a preferably highly volatile solvent or vehicle, such as methyl alcohol or amyl acetate.

. Referring to.=.-F.igure 6,. whiclnisialsectien taken at one of the wires, it will he seemthatzthe thickness of the coating is such that small points of metal are exposed at the outside of the cathode.

This practice is optional and is intended to reduce the resistance to heat conductivity through thecoating. The conductivity across the coating is increased by the presence of the metal, even i when: the: metal. does not project through, but

- the increase is greatest when it does.

tends toproduce holes, while a fine mesh tends to fill up solidly with the electron emissive material. Similarly, for a given mesh, the use of a fine, wire tends to produce holes, while the use of. a coarse Wire tends to prevent the formation of holes. This assumes the coating to. be the sam in all cases.

It is because of. the foregoing considerations that the general statement is made that the mesh of. the screen, the wire size of thescreen, and the thickness of the coatingmust all be properly interrelated and selected to produce the desired surface, whether it be a. waflie-like surface or a perforated surface.

Ina specific case I usedv a. IOU-mesh cathode.

screen made of 4 mil. nickel wire. The liquid.

coating was made thin enough to use in a spray, the cathode preferably being rotated while being sprayed. The final coating isbuilt up of a num ber of coats with drying periods therebetween.

With one or two coats and drying periods thecoating still had perforations therethrough. With three to five coats and drying periods, the holes were filled, but left with a waffle-like effect. With, say,.ten coats and drying periods, the final coat-- ing was built up to a level condition,.and the. de-.-. sired Waffle-like effect was lost.

It should be understood that the waffle effect is. a coarse roughness or irregularity different from a grainy texture or surface, the latter being obtainable even when using, a smooth metal can:

Most of the features and advantages of the present cathodelareo'btained when using a screen wrapped. closely. around a sheet metal can. I made cathodes of that type first, and may point outv the precaution thatthescreenrshould. preferablybe spotv welded. to. the: can at. numerous;- points. in. order'to, insure uniform heating oti the: screen and oxide mater-iaL, However, it.-is::-evem simpler tov eliminate. the sheet. metal. can and to use thescreen itself as.-the-.-can,, instead? of. merely; asa binder for the: oxide. materiaL Reverting, to Figure 2,. it. will be. understood that the grid ring. 3.0 is supportedmymeens of; suitable: lead-ins,, not show-n and; that the anodez l 6 alsoi supported. by appropriate lead-ins not: shown. If the electrode-assembly formsapartbf; an. oscillator tube. containing. resonantloops... the:- electrodesmay be. supported by thelssaidlloops.

, ThisJs-the. casevwhen theelectrode. assemblyis.v

used in aeso-called WI-158 tube, described. and; claimedgin. a copending applicatiomof: Harolda Zahl, Serial Number. 4573,5536,v filed. Januaryr zi, 1943, and. in a copencling. applicationv of; liarcldfm. Zahl, Glenn .Rouse, ,andsJohn-E. .(Imrha'm;v Seriall. Number 49.6,654-,.filed July 29., 1943,.Whi0h. as; Patent-N 0,. 2,454,298. on November; 23,, 848.

The; cathode l2; may. besupported; inpanw suit;- .able manner; but that-here showna's deemed-pref-'- erablea. 1'Ihe. cathode reenforcedlbgmeans;

0f.a:.ring 3'2 and this .-is.- carriedlon. .a;.tuhular; lead? in 34: on substantial. diameter saidleadein; beings secured-lcoaxiallysoflthe can .at-the-openend. thence-- of a filler? ringr 35 being: usedto make' upzfnr the! 1 difference.- in. diameter. between. the cathode and the tubulan'leadein. 'I hejheaten'filament is: supported and..-energizediby means loft asheatinsg. current lead.'-in.w-ire='38,-. which preferably-ma ns cow axially; through; the tubular leadsin 3h. 'Ihacem ten lead-inf wire. 3.8.: isvsealed: 81t-4B; '3|nd3 the entire: coaxial Elead-in .a-ss embly'ordinarily, passesthroughl andcisusealedztoraglasszstem projectingzontwardig from .the main. glass envelope-of. the: tulie.v The: large diameter tubular leadein. 31b be used;

I as=alradio frequ'encyrpath for cathodeztuning purposes, and 'is al's'o used asone side of tliea power: supply ci-rcu'it forheating the' filament 255 It is believedthat the methodofaccnstructing andusing-myimprcved' cathode; as. well"'as"-thi=:v ad vantages thereof; will be apparentfrom the" foregoing detailed description; Theelectronzemittihg" area is. substantially increased Without. increasing, the physical .area. of.' the cathode er g.,,,tlie.l'engtlil and diameter. in. the-case :of a cylindrical cathode; There. isa substantialreservoir, of electronemitting ,material corresponding,- to a.relatively; thick. oxide. coating, yet 1 the. oxide. materiaL is. securely held. by.. the screen. foundation, and. cannot. readily bIister ore fiake ofi... Holesmay lielprovided through the cathode if it is desired to heat the grid.

It will be apparent that while I have shown and described my invention in a preferred form, many changes and modifications may be made in the structure disclosed without departing from the spirit of the invention as sought to be defined in the following claims.

I claim:

1. A cathode for an electron emission tube, said cathode comprising a piece of wire screen made of high temperature metal bent to cylindrical configuration, and closed at one end by a disc, the opposite end being carried by a tubular lead-in of substantial diameter coaxial with the cathode, a heater filament inside said cathode, a lead-in wire for said heater filament passing oaxially through the aforesaid tubular lead-in, and a coating of metal oxide electron emissive material applied in varying thickness to the aforesaid cylindrical screen.

2. A cathode for an electron emission tube, said cathode comprising a piece of wire screen of high temperature metal bent to cylindrical configuration, and closed at one end by a disc, the opposite end being carried by a tubular lead-in of substantial diameter coaxial with the cathode, a heater filament inside said cathode, a lead-in wire for said heater filament passing coaxially through the aforesaid tubular lead-in, and a coating of metal oxide electron emissive material applied to the aforesaid cylindrical screen, said screen having a roughened waffle-like surface on the outside of the cathode, thereby increasing the electron emitting area of the cathode for a given length and diameter of cathode can.

3. An electrode assembly comprising a cylindrical cathode, a cylindrical grid surrounding said cathode, and a cylindrical anode surrounding said grid, said cathode comprising a piece of Wire screen of high temperature metal bent to cylindrical configuration, and closed at one end by a disc, the opposite end being carried by a tubular lead-in of substantial diameter coaxial with the cathode, a heater filament inside said cathode, a lead-in wire for said heater filament passing coaxially through the aforesaid tubular lead-in, and a coating of metal oxide electron emissive material applied to the aforesaid cylindrical screen to completely eover said wire screen.

GLENN F. ROUSE.

REFERENCES CITED lhe following references are of record in the file of this patent:

UNITED STATES PATENTS Great Britain Sept. 21, 1936 

